Molecular Engineering Using an Anthanthrone Dye for Low-Cost Hole Transport Materials: A Strategy for Dopant-Free, High-Efficiency, and Stable Perovskite Solar Cells

In this report, highly efficient and humidity-resistant perovskite solar cells (PSCs) using two new small molecule hole transporting materials (HTM) made from a cost-effective precursor anthanthrone (ANT) dye, namely, 4,10-bis(1,2-dihydroacenaphthylen-5-yl)-6,12-bis(octyloxy)-6,12-dihydronaphtho[7,8,1,2,3-nopqr] tetraphene (ACE-ANT-ACE) and 4,4'-(6,12-bis(octyloxy)-6,12-dihydronaphtho[7,8,1,2,3-nopqr] tetraphene-4,10-diyl) bis(N, N-bis(4-methoxyphenyl) aniline) (TPA-ANT-TPA) are presented. The newly developed HTMs are systematically compared with the conventional 2,2',7,7'-tetrakis(N, N'-di-p-methoxyphenylamino)-9,9'-spirbiuorene (Spiro-OMeTAD). ACE-ANT-ACE and TPA-ANT-TPA are used as a dopant-free HTM in mesoscopic TiO2/CH3NH3PbI3/HTM solid-state PSCs, and the performance as well as stability are compared with Spiro-OMeTAD-based PSCs. After extensive optimization of the metal oxide scaffold and device processing conditions, dopant-free novel TPA-ANT-TPA HTM based PSC devices achieve a maximum power conversion efficiency (PCE) of 17.5% with negligible hysteresis. An impressive current of 21 mA cm(-2) is also confirmed from photocurrent density with a higher fill factor of 0.79. The obtained PCE of 17.5% utilizing TPA-ANT-TPA is higher performance than the devices prepared using doped Spiro-OMeTAD (16.8%) as hole transport layer at 1 sun condition. It is found that doping of LiTFSI salt increases hygroscopic characteristics in Spiro-OMeTAD; this leads to the fast degradation of solar cells. While, solar cells prepared using undoped TPA-ANT-TPA show dewetting and improved stability. Additionally, the new HTMs form a fully homogeneous and completely covering thin film on the surface of the active light absorbing perovskite layers that acts as a protective coating for underlying perovskite films. This breakthrough paves the way for development of new inexpensive, more stable, and highly efficient ANT core based lower cost HTMs for cost-effective, conventional, and printable PSCs.